This is a competing renewal application that builds on the instrumentation and expertise developed in the course of the previous funding periods. We propose to investigate the feasibility of extending the current magnetic cell separation methods to applications relying on the cell's own, natural (intrinsic) magnetization. The application rests on the hypothesis that there is a link between malignant cell transformation and an increase in the cell magnetic susceptibility. The supporting evidence comes from a large body of data from other studies on the magnetic properties of tissues, in particular, from electron (spin) paramagnetic resonance, EPR, and studies of solid tumors. Additional supporting evidence comes from our own data on the magnetic field-induced motion (magnetophoresis) in physiologic electrolyte solutions of cancer cell lines (HeLa and Hep 3B), that demonstrate statistically greater velocity compared to controls (oxygenated red blood cells). We have shown an additional increase in the cell magnetophoretic mobility following the addition of soluble iron compounds to the culture media, suggesting an effect of intracellular iron uptake on the cell magnetization. The proposed effort is divided between: Specific Aims: SA1: To investigate the molecular mechanism for the observed increase in magnetophoretic mobility (MM) in selected cancer cell lines as compared to matched normal cells. In collaboration with experts in cell tracking velocimetry (Dr. Chalmers) and EPR spectrometry (Dr. Kuppusamy) at the subcontract site (The Ohio State University), the effect of iron in the medium on the cell magnetophoretic mobility and the increased intracellular paramagnetic content will be investigated on cancer cell lines. SA2: To improve the sensitivity and resolution of the cell magnetophoretic mobility analyzer, the Cell Tracking Velocimetry (CTV). The increase of magnetophoretic mobility resolution by a factor up to 10 fold will be accomplished by increasing the magnetic energy density and field gradient of the apparatus, by improving the imaging capability of the cell tracking hardware and software, and by including corrections for fluid dynamics artifacts in collaboration with an expert in field-flow fractionation (Dr. Williams). SA3: To measure the magnetic susceptibility of selected primary tumors at a single cell level against a baseline of normal blood cells. Primary tumor cell lines will be tested against normal controls for differences in the magnetophoretic mobility, in collaboration with an expert oncologist (Dr. Borden). SA4: To test the feasibility of the label-less, magnetic cancer cell separation on model blood cell suspensions. The proposed strategy is based on the soluble - rather than particulate - iron transport processes, and may therefore be more finely tuned to the pathobiology of the cancer cell than is practiced today. It could have a profound impact on how the magnetic cell separation is practiced and utilized and could complement and extend the applications of the already existing magnetic cell separation methods.